The present invention relates to an oscillation mechanism for chairs comprising an adjustment system of the oscillation of a structure of a chair, which allows to change the intensity of the reaction that the system opposes to a given oscillation exerted by the user.
Chairs are known, in particular for office, which comprises a support frame coupled to floor prop means, and at least one oscillating structure with respect to the support frame. This structure can be, for example, the seat support and/or the backrest support of the chair. In some embodiments, the seat support and the backrest support are rigidly coupled between themselves and oscillate as one, in others embodiments the seat support and the backrest support are both oscillating with respect to the frame in an independent way or in a way reciprocally coupled but not rigidly.
When the oscillating structure oscillates under the thrust of the user, the chair opposes an elastic reaction which tends to bring back the chair in its rest position (without thrust). This reaction is typically realized by an elastic element, for example a spring.
Adjustment systems of the oscillation are also known, which can adjust, according to the user's preferences, the intensity of the reaction torque which the chair opposes to a given oscillation, and which has to be balanced by the user.
The Applicant has nonetheless discovered that some known adjustment systems are not efficient in transferring the forces involved and/or are not adjustable comfortably by the user.
According to the Applicant some known adjustment systems are structurally complex and/or complex to be used, and/or bulky and/or heavy and/or expensive to be produced.
For example, the Applicant has considered that known adjustment systems can show a size and/or a weight and/or a cost such that they cannot be used in those applications for which the chair has to comply size and/or weight and/or cost limits.
The Applicant has also perceived the problem of preventing that the actuation member of the adjustment must undergo a very wide excursion to bring the chair from a configuration of maximum stiffness to a configuration of maximum softness of the chair reaction. In fact, said wide excursion can create discomfort to the user.